Necessary and sufficient conditions are given for projective plane curves to have cusps isomorphic to the origin of an affine plane curve xa + yb. Based on them, a family of curves Cab having only one such cusp as a singular point and a family of curves rCab having only two such cusps as singular points are formulated. Also, the structures of algebraic geometric codes generated on curves contained in these families are shown, where a and b are relatively prime. Then the genus is (a − 1)/(b − 1)/2 and the basis of linear space L(m · P) is given by rational functions xiyi only. Second, by giving concrete examples, it is shown that families of curves Cab and rCab contain many curves which attain Hasse‐Weil upper bound.

The essence of money circulation is that money continues to transfer among economic agents eternally. Based on this recognition, this paper shows a money circulation equation that calculates the quantities of expenditure, revenue, and the end money from the quantity of the beginning money. The beginning money consists of the possession at term beginning, production and being transferred from the outside of the relevant society. The end money consists of the possession at term end, disappearance and transferring to the outside of the relevant society. This equation has a unique solution if and only if each part of the relevant society satisfies the space-time openness condition. Moreover, if money is transferred time irreversibly, each part of the relevant society satisfies the space-time openness condition. Hence, the solvability of the equation is guaranteed by time irreversibility. These solvability conditions are similar to those of the economic inputoutput equation, but the details are different. An equation resembling our money circulation equation was already shown by Mária Augustinovics, a Hungarian economist. This paper examines the commonalities and differences between our equation and hers. This paper provides the basis for some intended papers by the author.

Under the assumption that we have defining equations of an affine algebraic curve in special position with respect to a rational place Q, we propose an algorithm computing a basis of L(D) of a divisor D from an ideal basis of the ideal L(D + ∞Q) of the affine coordinate ring L(∞Q) of the given algebraic curve, where. Elements in the basis produced by our algorithm have pairwise distinct discrete valuations at Q, which is convenient in the construction of algebraic geometry codes. Our method is applicable to a curve embedded in an affine space of arbitrary dimension, and involves only the Gaussian elimination and the division of polynomials by the Gröbner basis for the ideal defining the curve.

In a monetary economy, expenditure induces revenue for each agent. We call this the revenue induction phenomenon. Moreover, in a special case, part of the expenditure by an agent returns as their own revenue. We call this the expenditure reflux phenomenon. Although the existence of these phenomena is known from the olden days, this paper aims to achieve a more precise quantification of them. We first derive the revenue induction formula through solving the partial money circulation equation. Then, for a special case, we derive the expenditure reflux formula. Furthermore, this paper defines the revenue induction coefficient and the expenditure reflux coefficient, which are the key concepts for understanding the two formulas, and examines their range.